It is known in the art relating to internal combustion engines that modern vehicle engine designs utilize engine oil pressure to enable various forms of variable engine valve actuation devices, including cam phasers and cylinder deactivation devices. Such variable valve actuation devices have strict pressure requirements. For example, cam phasers require a certain minimum pressure for proper function, while an excess pressure condition can cause cylinder deactivation system malfunction. Due to the strict pressure requirements of these devices, use of these devices has created a very narrow operational pressure window for the lubrication system of the engine.
Previously, in U.S. Pat. No. 6,763,797, we disclosed a variable displacement pump in which pump outlet pressure is used to bias the position of a cam ring (slide), thereby changing the eccentricity of the pump and consequently varying the pump displacement. By varying the pump displacement relative to pump outlet pressure, the pump outlet pressure can be controlled based on engine flow requirements. The pressure regulation characteristics of the pump are determined by calibrating a reaction spring that counterbalances the hydraulic forces acting on the cam ring. Further optimization of the pressure regulation characteristics of variable displacement pumps used in engine lubrication systems is desirable.